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Area Geology

Finger Lakes

The Finger Lakes are eleven glacially formed lakes in western New York, mainly linear in shape with a north-south orientation. They include Otisco Lake, Skaneateles Lake, Owasco Lake, Cayuga Lake, Seneca Lake, Keuka Lake, Canandaigua Lake, Honeoye Lake, Canadice Lake, Hemlock Lake and Conesus Lake. The longest, Cayuga Lake, is 40 miles from end to end, but never more than 3.5 miles wide and not atypical in shape, reminding early map-makers of the fingers of a hand. Considering their narrow width, both Cayuga and Seneca Lakes have a remarkable trait; they rival much larger Lake Ontario for depth, each more than 400 feet.
Today the Finger Lakes area is still known for fishing and hunting. Winter sports are also popular, with skiing, snowmobiling and ice fishing available.

Keuka Lake

Located in the heart of central New York wine country, Keuka Lake lies 17 miles southwest of the City of Geneva. Keuka Lake is a unique member of the Finger Lakes because it’s unique ‘Y’ shape instead of the other long and narrow shaped lakes. Because of its shape, it is often referred to as the Crooked Lake.

Keuka lake ranks third in size among the Finger Lakes (behind Cayuga and Seneca Lakes). The hamlet of Branchport is located at the tip of the lake’s northwest arm and the Village of Penn Yan tips the northeast arm. At the lake’s south end is the Village of Hammondsport (the home of aviation pioneer Glenn Curtiss, the Father of Naval Aviation).

Physical Features
Elevation: 715 feet
Area: 11,584 acres
Length: 19.6 miles
Maximum width: 1.9 miles
Maximum depth: 183 feet
Thermocline: between 30-35 feet
Water Quality: very clear and well oxygenated at all depths.

Keuka Lake serves as a public water supply for Hammondsport, Branchport, Penn Yan and Keuka College.

The Keuka Lake region belongs to a topographic province called the Allegheny Plateau. The shale and sandstone formations found here represent mud and sand deposits that settled on a shallow sea floor over millions of years. These sediments gradually became rock under the pressure of successive layers in a process called lithification. Many area gorges and glens contain fossils such as trilobites, brachiopods, and corals. Geologically speaking, the surface rocks belong to the West River Group and are sandstones, siltstones, and shales originating from the erosion of the Acadian Mountains to the east. These mountains were a product of the collision of the North American and Avalonian Plates. The region first became dry land more than 300 million years ago during late Devonian times. A long period of uplift and erosion began. During this time, about one vertical mile of rock material was eroded from the original two-mile-thick stack by a system of rivers that developed in the area. One such river occupied the Keuka valley.

The Ice Age or Pleistocene Period began about two million years ago, bringing a succession of glacial ice sheets from the north. Evidence has been found indicating there were at least 10 and possibly 20 distinct cold periods that could have resulted in an ice sheet advance and subsequent melt-off. Each glacier scoured the landscape under its enormous weight and removed rock material, erasing evidence of the preceding glacier. The continental ice sheets slowly flowed into existing river valleys as valley glaciers, massively reshaping the topography. The valleys running north-south were greatly deepened and changed from a V-shaped cross-section to a U-shaped one by the south- flowing ice. As the advancing ice sheet thickened, ridges between the glacially deepened valleys were sculpted by the flowing ice into streamlined forms as seen in the ridges between the east and west branches of Keuka Lake. The last continental glacier was at least one mile thick.

As the last glacier slowly melted and retreated northward, it stalled about 17,000 years ago for a period of time and dumped what has been called the Valley Heads Moraine. This formed a barrier preventing southward drainage of glacial meltwaters. A part of this barrier remains today as the hilly topography between Hammondsport and Bath.
Around 15,000 years ago the water level in the Keuka valley rose to about 1,000 feet above sea level, causing an overflow of the west branch into the east branch. As water flowed between the present day Keuka Lake State Park and Route 54A, the Bluff became an island for about 300 years. Meanwhile, meltwater continued to flow over the ridge from Keuka Lake to Seneca Lake, eventually forming the present outlet between them. Keuka’s level gradually lowered to its present elevation of approximately 714 feet above sea level.

When underlying shale layers were eroded, harder sandstone on the Bluff’s crest resisted. As ancient rivers flowed around the Bluff, it remained creating today’s Y shape. Major inlets to Keuka Lake are located at Hammondsport and Branchport. The outlet is in Penn Yan, where the lake level is regulated by a set of gates. From this outlet, water drains to Seneca Lake and then northward through the Seneca-Oswego-Oneida Rivers Drainage Basin, eventually reaching the Atlantic Ocean via Lake Ontario and the St. Lawrence River.
The highest points in the Town of Jerusalem are on the Bluff and the Pinnacle (the hill behind you), each about 1,400 feet above sea level. There are spectacular views from Esperanza Road and along Skyline Drive.

Glaciers followed existing streambeds leaving Keuka as a “Y”-shaped lake as they receded. (Black lines show where the southern edge of the last receding glacier was 17,000 years ago.) About 15,000 years ago, the water rose so high that the Bluff became an island for about 300 years.

Isachsen,Y.W., E. Landing, J.M. Lauber, L.V. Rickard, and W. B. Rogers, Geology of New York, New York State Education Department, 2000
New York State Geological Association 58th Annual Meeting Field G, New York State Geological Association, 1986
USGS Quad Sheet, Lake Level
Van Diver, Bradford B., Upstate New York: K/H Geology Field Guide Series, Kendall/Hunt Publishing, 1980
Von Engeln, O.D., The Finger Lakes Region, Cornell University Press 1961